The present invention generally relates to an apparatus and a method for mounting a rotational disk and more particularly, relates to an apparatus and a method for mounting a conditioning disk onto a conditioning head for use in a chemical mechanical polishing apparatus that is capable of preventing slurry from being siphoned into the control system.
Apparatus for polishing thin, flat semi-conductor wafers is well-known in the art. Such apparatus normally includes a polishing head which carries a membrane for engaging and forcing a semiconductor wafer against a wetted polishing surface, such as a polishing pad. Either the pad, or the polishing head is rotated and oscillates the wafer over the polishing surface. The polishing head is forced downwardly onto the polishing surface by a pressurized air system or, similar arrangement. The downward force pressing the polishing head against the polishing surface can be adjusted as desired. The polishing head is typically mounted on an elongated pivoting carrier arm, which can move the pressure head between several operative positions. In one operative position, the carrier arm positions a wafer mounted on the pressure head in contact with the polishing pad. In order to remove the wafer from contact with the polishing surface, the carrier arm is first pivoted upwardly to lift the pressure head and wafer from the polishing surface. The carrier arm is then pivoted laterally to move the pressure head and wafer carried by the pressure head to an auxiliary wafer processing station. The auxiliary processing station may include, for example, a station for cleaning the wafer and/or polishing head, a wafer unload station, or a wafer load station.
More recently, chemical-mechanical polishing (CMP) apparatus has been employed in combination with a pneumatically actuated polishing head. CMP apparatus is used primarily for polishing the front face or device side of a semiconductor wafer during the fabrication of semiconductor devices on the wafer. A wafer is xe2x80x9cplanarizedxe2x80x9d or smoothed one or more times during a fabrication process in order for the top surface of the wafer to be as flat as possible. A wafer is polished by being placed on a carrier and pressed face down onto a polishing pad covered with a slurry of colloidal silica or alumina in de-ionized water.
A schematic of a typical CMP apparatus is shown in FIGS. 1A and 1B. The apparatus 20 for chemical mechanical polishing consists of a rotating wafer holder 14 that holds the wafer 10, the appropriate slurry 24, and a polishing pad 12 which is normally mounted to a rotating table 26 by adhesive means. The polishing pad 12 is applied to the wafer surface 22 at a specific pressure. The chemical mechanical polishing method can be used to provide a planar surface on dielectric layers, on deep and shallow trenches that are filled with polysilicon or oxide, and on various metal films. CMP polishing results from a combination of chemical and mechanical effects. A possible mechanism for the CMP process involves the formation of a chemically altered layer at the surface of the material being polished. The layer is mechanically removed from the underlying bulk material. An altered layer is then regrown on the surface while the process is repeated again. For instance, in metal polishing a metal oxide may be formed and removed repeatedly.
A polishing pad is typically constructed in two layers overlying a platen with the resilient layer as the outer layer of the pad. The layers are typically made of polyurethane and may include a filler for controlling the dimensional stability of the layers. The polishing pad is usually several times the diameter of a wafer and the wafer is kept off-center on the pad to prevent polishing a non-planar surface onto the wafer. The wafer is also rotated to prevent polishing a taper into the wafer. Although the axis of rotation of the wafer and the axis of rotation of the pad are not collinear, the axes must be parallel.
The polishing pad is a consumable item used in a semiconductor wafer fabrication process. Under normal wafer fabrication conditions, the polishing pad is replaced after about 12 hours of usage. Polishing pads may be hard, incompressible pads or soft pads. For oxide polishing, hard and stiffer pads are generally used to achieve planarity. Softer pads are generally used in other polishing processes to achieve improved uniformity and smooth surface. The hard pads and the soft pads may also be combined in an arrangement of stacked pads for customized applications.
A problem frequently encountered in the use of polishing pads in oxide planarization is the rapid deterioration in oxide polishing rates with successive wafers. The cause for the deterioration is known as xe2x80x9cpad glazingxe2x80x9d wherein the surface of a polishing pad becomes smooth such that the pad no longer holds slurry in-between the fibers. This is a physical phenomenon on the pad surface not caused by any chemical reactions between the pad and the slurry.
To remedy the pad glazing effect, numerous techniques of pad conditioning or scrubbing have been proposed to regenerate and restore the pad surface and thereby, restoring the polishing rates of the pad. The pad conditioning techniques include the use of silicon carbide particles, diamond emery paper, blade or knife for scrapping the polishing pad surface. The goal of the conditioning process is to remove polishing debris from the pad surface, re-open the pores, and thus forms micro-scratches in the surface of the pad for improved life time. The pad conditioning process can be carried out either during a polishing process, i.e. known as concurrent conditioning, or after a polishing process.
A conventional conditioning disc for use in pad conditioning is shown in FIG. 1C in a perspective view of a CMP apparatus 50. The apparatus 50 consists of a conditioning head 52 which includes a conditioning disc 68 mounted to a hub frame 70, a polishing pad 56, and a slurry delivery arm 54 positioned over the polishing pad. The conditioning head 52 is mounted on a cover ring 58 which is extended over the top of the polishing pad 56 for making sweeping motion across the entire surface of the pad. The slurry delivery arm 54 is equipped with slurry dispensing nozzles 62 which are used for dispensing a slurry solution on the top surface 60 of the polishing pad 56. Surface grooves 64 are further provided in the top surface 60 to facilitate even distribution of the slurry solution and to help entrapping undesirable particles that are generated by coagulated slurry solution or any other foreign particles which have fallen on top of the polishing pad during a polishing process.
FIG. 2 shows a cross-sectional view of the conditioning head 52 of FIG. 1C. The conditioning head 52 is constructed by a bearing mount 42, a ball-bearing 44, a cylinder rotator 46, and a cylinder shaft 48. The bearing mount 42 and the ball-bearings 44 are mounted stationarily, while the cylinder rotator 46 and the cylinder shaft rotate when driven by a pulley 40. A pneumatic conduit 52 is utilized to supply a pressure onto the cylinder shaft 48 such that a conditioning disk 54 is pushed downwardly onto the surface of a polishing pad to be conditioned. The pneumatic conduit 52 further supplies a negative pressure, i.e. a vacuum onto the cylinder shaft 48, when the conditioning motion of the conditioning disk 54 is to be stopped and that the conditioning disk 54 is to be disengaged from the surface of the polishing pad. An elastomeric diaphragm 36 is used to provide a fluid seal between the cylinder shaft 48 and the cylinder rotator 46 to prevent the back flow of polishing slurry into the pneumatic conduit 52.
In the conventional design of the polishing head shown in FIG. 2, numerous design deficiencies have been discovered which may lead to serious processing difficulties. For instance, firstly, the conditioning head may have a short lifetime of less than one month, due to a breakage or fracture of the elastomeric diaphragm in the conditioning head due to the fact that the diaphragm is continuously moved inwardly and downwardly during disengagement and engagement of the conditioning head from and to a polishing pad. Secondly, since there is not a reliable method for detecting when the elastomeric diaphragm may fail or break, unstable downward pressure on the conditioning head frequently results which leads to inconsistent conditioning results. Thirdly, when the elastomeric diaphragm fractures or breaks, slurry solution may be siphoned back into the vacuum system to block the vacuum conduits, the pneumatic valves and the vacuum source. Fourthly, since the conditioning head is mechanically fixed to the cylinder shaft and that the available space between the two is very small, it is difficult to remove and replace the diamond disk mounted on the conditioning disk when necessary.
It is therefore an object of the present invention to provide an apparatus for mounting a rotational disk to a stationary bearing mount with ball-bearings that does not have the drawbacks or shortcomings of the conventional apparatus.
It is another object of the present invention to provide an apparatus for mounting a conditioning disk in a conditioning head in a chemical mechanical polishing apparatus that does not have a reliability problem.
It is a further object of the present invention to provide an apparatus for mounting a conditioning disk in a conditioning head for a chemical mechanical polishing apparatus which utilizes a cylinder shaft and a piston affixed to the shaft for preventing any leakage of slurry solution through the conditioning head.
It is another further object of the present invention to provide an apparatus for mounting a conditioning disk in a conditioning head for a chemical mechanical polishing apparatus wherein a cylinder shaft is equipped with a universal connector for connecting to a disk holder for the conditioning disk.
It is still another object of the present invention to provide an apparatus for mounting a conditioning disk in a conditioning head for a chemical mechanical polishing apparatus wherein a universal connector is used to mount the conditioning disk allowing a tilting motion of the conditioning disk.
It is yet another object of the present invention to provide an apparatus for mounting a conditioning disk in a conditioning head for a chemical mechanical polishing apparatus in which a piston and a gasket is utilized to prevent any possible leakage of a slurry solution through the conditioning head.
It is still another further object of the present invention to provide an apparatus for mounting a conditioning disk in a conditioning head for a chemical mechanical polishing apparatus wherein the use of an elastomeric diaphragm between a cylinder shaft and a cylinder rotator is eliminated.
It is yet another further object of the present invention to provide a method for mounting a conditioning disk in a conditioning head for a chemical mechanical polishing apparatus by mounting a cylinder shaft to a cylinder rotator through a piston and a gasket and a disk holder to the cylinder shaft by a universal connector.
In accordance with the present invention, an apparatus and a method for mounting a conditioning disk in a conditioning head for a chemical mechanical polishing apparatus are provided.
In a preferred embodiment, an apparatus for mounting a conditioning disk in a chemical mechanical polishing apparatus is provided which includes a torroidal-shaped bearing mount for fixedly mounting to a conditioning arm in a CMP apparatus, the torroidal-shaped bearing mount is adapted for receiving a ball bearing and a cylinder rotator that turns on the ball bearing; a cylinder rotator that has a cylinder chamber therein defined by a top wall and a bottom wall with center apertures therethrough for receiving a cylinder shaft; a cylinder shaft that has a piston mounted juxtaposed to a top end and a universal connector at a bottom end, the cylinder shaft may be mounted through the center apertures of the cylinder rotator, the piston may further include a gasket for sealing between the piston and an interior surface of the cylinder chamber wall; a disk holder for mounting to the universal connector on the cylinder shaft through a universal mount located in a top surface of the disk holder such that the disk holder may tilt and follow the contour of a polishing pad through a conditioning disk mounted thereon while rotated by the cylinder rotator; and a pneumatic means for applying to the cylinder shaft and for enabling an up-and-down motion of the cylinder shaft.
In the apparatus for mounting a conditioning disk in a CMP machine, the piston frictionally engages the interior chamber wall of the cylinder rotator by the gasket. The gasket on the piston may be fabricated of an elastomeric material for providing frictional engagement between the piston and the interior chamber wall of the cylinder rotator. The apparatus may further include a diamond disk mounted to a bottom surface of the disk holder. The apparatus may further include a pulley for driving the cylinder rotator and causing it to rotate. The universal connector enables the disk holder to tilt at least xc2x130xc2x0 from a horizontal plane. The cylinder rotator, the cylinder shaft and the disk holder rotate as a single unit. The pneumatic means is operable by an air pressure of at least 5 psi for pressing the disk holder downwardly to engage a diamond disk to a polishing pad. The pneumatic means may be operable by air pressure of not higher than xe2x88x9210 psi for moving the disk holder upwardly to disengage a diamond disk from a polishing pad. The ball bearing may be fixedly mounted to the bearing mount on a conditioning arm.
The present invention is further directed to a method for mounting a conditioning head in a chemical mechanical polishing machine which can be carried out by the operating steps of first providing a torroidal-shaped bearing mount fixedly mounted to a conditioning arm in a CMP apparatus; providing a cylinder rotator that has a cylinder chamber therein defined by a top wall and a bottom wall with center apertures for receiving a cylinder shaft; mounting the cylinder rotator to the bearing mount with a ball bearing therein-between; providing a cylinder shaft that has a piston fixed thereon juxtaposed to a top end and a universal connector at a bottom end, the piston may further include a gasket for sealing between the piston and an interior surface of the cylinder chamber wall; mounting the cylinder shaft inside the cylinder rotator through the center apertures in the top wall and the bottom wall with the gasket frictionally engaging the interior surface of the cylinder chamber wall; providing and mounting a disk holder to the universal connector on the cylinder shaft by a universal mount located at a center of the disk holder such that the disk holder tilts and follows the contour of a polishing pad with a conditioning disk mounted thereon and when the disk holder is rotated by the cylinder shaft; and applying a pneumatic pressure to the cylinder shaft and moving the cylinder shaft in an up-and-down motion.
The method for mounting a conditioning head in a CMP apparatus may further include the step of mounting the gasket on an outer rim of the piston, or the step of fabricating the gasket from an elastomeric material and providing a fluid seal for slurry solution between the piston and the interior chamber wall of the cylinder rotator, or the step of mounting a diamond disk to a bottom surface of the disk holder. The method may further include the step of rotating the cylinder rotator by a pulley. The universal connector enables the disk holder to tilt to a maximum of at least xc2x130xc2x0 from a horizontal plane. The method may further include the step of rotating the cylinder rotator, the cylinder shaft and the disk holder together as a single unit, or the step of applying a pneumatic pressure of at least 5 psi for pressing the disk holder downwardly to engage a diamond disk to a polishing pad, or the step of applying a pneumatic pressure of not higher than xe2x88x9210 psi for moving the disk holder upwardly to disengage a diamond disk from a polishing pad. The method may further include the step of fixedly mounting the ball bearing to the bearing mount on the conditioning arm.